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add tapering to ft8_downsample.f90
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@ -5,13 +5,22 @@ subroutine ft8_downsample(dd,newdat,f0,c1)
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parameter (NMAX=15*4000,NSPS=640)
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parameter (NFFT1=64000,NFFT2=3200) !64000/20 = 3200
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logical newdat
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logical newdat,first
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complex c1(0:NFFT2-1)
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complex cx(0:NFFT1)
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complex dd(NMAX),x(NFFT1)
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real taper(0:100)
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equivalence (x,cx)
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save cx
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data first/.true./
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save cx,first,taper
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if(first) then
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pi=4.0*atan(1.0)
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do i=0,100
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taper(i)=0.5*(1.0+cos(i*pi/100))
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enddo
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first=.false.
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endif
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if(newdat) then
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! Data in dd have changed, recompute the long FFT
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x(1:NMAX)=dd
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@ -24,9 +33,9 @@ subroutine ft8_downsample(dd,newdat,f0,c1)
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df=4000.0/NFFT1
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baud=4000.0/NSPS
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i0=nint(f0/df)
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ft=f0+8.0*baud
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ft=f0+8.5*baud
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it=min(nint(ft/df),NFFT1)
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fb=f0-1.0*baud
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fb=f0-1.5*baud
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ib=max(1,nint(fb/df))
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k=0
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c1=0.
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@ -34,6 +43,8 @@ subroutine ft8_downsample(dd,newdat,f0,c1)
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c1(k)=cx(i)
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k=k+1
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enddo
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c1(0:100)=c1(0:100)*taper(100:0:-1)
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c1(k-1-100:k-1)=c1(k-1-100:k-1)*taper
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c1=cshift(c1,i0-ib)
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call four2a(c1,NFFT2,1,1,1) !c2c FFT back to time domain
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fac=1.0/sqrt(float(NFFT1)*NFFT2)
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